whitest county Biden won, least white county Trump won

[mileslunn]

Wondering if anyone knows the answer to this.  For years it was Elliott County, Kentucky but that is now solidly GOP.  I believe Bush in 2004 won a few minority-majority ones and Trump may have.  He did win some majority Hispanic ones in Rio Grande Valley but not sure if he won any African-American majority.  Romney and McCain won none of those.  For least white Trump won, it would be good to have both for non-Hispanic whites and just non-whites as in Rio Grande Valley many are both white and Hispanic.

[H. Ross Peron]

Windsor County, VT?

[Alcibiades]

Lake County, MN was the whitest county which Clinton won in 2016, and I assume also the whitest that Biden carried.

[lfromnj]

Least white Trump won is Zapata County if you count Hispanics as non white.
Otherwise its Robeson ?

[Roll Roons]

Lake County, MN was the whitest county which Clinton won in 2016, and I assume also the whitest that Biden carried.

Probably, unless there's some even whiter county he won in Vermont or Maine. Not counting the RGV, the least white county Trump won was probably some rural county in the South that's majority white, but has around a 30-40% black population.

[Alcibiades]

Actually, I must correct myself: Biden flipped Carroll County, NH, which according to Census Bureau estimates is 0.3pp non-Hispanic whiter than Lake, MN, at 95.6%.

[Wormless Gourd]

If you consider self-identified white hispanics(90% of the population) to not actually be white, then Zapata county. Question solved.
If you take them at their word, then the least white county-equivalent Trump won may be Aleutians East Borough, which is <10% non-hispanic white or ~<20% white including white hispanics. Trump winning this borough is an estimate through @cinyc9 on Twitter who is seasoned at creating borough-level results and the racial data is also an estimate by the census website, which can likely be quite off with Alaska borough-level data. So a double estimate if you wanted to use Alaska's boroughs in this.
If you want only mainland US counties and consider white hispanics to be white, then it may be Robeson, at 30.6% white/24.7% white non-hispanic. It could also be Corson, SD, which 0.3% less white then Robeson when including white hispanics(30.2%) but has a higher share of non-hispanic whites then Robeson(29%). The census is going to be finished next year and this is well within the possibility of being very slightly off for one or both, as the census site only provides an estimate for the racial composition of these counties.
So the least white county that Trump won is either in South Texas, Alaska, southeastern NC or within the Standing Rock Indian Reservation, depending on your criteria.